(1) Field of the Invention
The present invention relates to a hemispherical dynamic pressure bearing and, more particularly, to a semi-spherical bearing having gap adjusting means for adjusting a gap between a pair of hemispheres disposed facing one another so that the bearing operates in an optimal state.
(2) Brief Description of Related Art
Generally, a dynamic pressure bearing comprises a supporter, and a rotating member eccentrically and rotatably supported by the supporter. Pressure is formed by lubricant fluid within a gap defined between the supporter and the rotating member so as to enhance the rotation of the rotating member.
Particularly, a hemispherical dynamic bearing is designed such that a portion thereof for supporting the rotating member is hemispherically-shaped so as to simultaneously support a radial load and a thrust load.
Accordingly, since there is no need for a plurality of bearings for supporting each load, it is possible to make the bearing compact. In addition, when using air as the fluid for forming lubricant pressure for the dynamic bearing, a seal member is not required such that the bearing can be made in a more compact state. This compact bearing is suitable for use in a motor used in electronic products.
Referring to FIG. 4, there is shown a sectional view illustrating a motor where a conventional hemispherical dynamic pressure bearing for rotating a multi-faceted mirror used in a laser scanning unit is provided.
The multi-faceted mirror 1 reflects laser beams, scanned by a semiconductor laser, to a photoconductive drum. The motor 2 is employed to rotate the multi-faced mirror 1.
As shown in FIG. 4, the multi-faceted mirror 1 is coupled to a rotating member 1a, while the rotating member 1a is coupled to a bushing 8 of a hemispherical dynamic pressure bearing 9.
There is provided a frame 2a disposed under the motor 2. A supporting shaft 3 is coupled on a center of the frame 2a and extends upward. A sliding hemisphere 5 is slidably disposed on the supporting shaft 3 which extends through an axial hole 5a of the sliding hemisphere 5, while a fixed hemisphere 4 is snugly disposed on the supporting shaft 3 which extends through an axial hole 4a of the fixed hemisphere 4. The fixed hemisphere 4 is located under the sliding hemisphere 5.
The sliding and fixed hemispheres 5 and 4 are arranged such that their planar surfaces are directed upward and downward, respectively. A sleeve 6 is disposed around the supporting shaft 3 between the sliding and fixed hemispheres 5 and 4 so as to establish the distance between the hemispheres 5 and 4. That is, the hemispheres 5 and 4 closely contact the sleeve 6 such that the sliding hemisphere 5 is spaced away from the fixed hemisphere 4 by a longitudinal length of the sleeve 6.
A fixing ring 7 is coupled around the supporting shaft 3 above the sliding hemisphere 5 such that it can fix the hemispheres 5 and 4, and the sleeve 6.
The hemispheres 5 and 4 and the sleeve 6 are enclosed by the bushing 8. That is, the bushing 8 is provided at its upper and lower ends with hemispherical grooves 8b and 8a complemental to the hemispheres 5 and 4, respectively, and a communicating hole 8c connecting the hemispherical grooves 8b and 8a to each other. The sleeve 6 is positioned in the communicating hole 8c so that it can rotate with respect to the hemispheres 5 and 4.
A rotor 2b is attached on an outer circumference of the bushing 8, while a stator 2c is coupled to an inner circumference of the frame 2a and extended toward the rotor 2b.
In the above described motor 2, the dynamic pressure bearing 9 comprising the supporting shaft 3, the hemispheres 5 and 4, and the bushing 8 has gaps defined between the hemispheres 5 and 4 and the hemispherical grooves 8b and 8a, which can be adjusted by adjusting the distance between the sliding hemisphere 5 and the fixed hemisphere 4.
However, if the hemispherical dynamic pressure bearing is assembled incorrectly or is used for a long time, an improper gap may result. If the bearing is further used in this state, wherein the hemispheres contact the hemispherical grooves, the contacting surfaces become worn, thereby generating noise or forming dynamic pressure ineffectively. Therefore, in such a case, the gaps between the hemispherical grooves and the hemispheres should be adjusted by replacing the sleeve 6 with a sleeve of different length.
However, in the prior bearing, since the sleeve is retained by the fixing ring 7, it is necessary to disassemble the bearing and detach the sleeve, in order for a sleeve of different length to be inserted. Then, the parts must be reassembled which is a troublesome and time-consuming task.